Brain Pathology Case of the Month - March 2000

FINAL DIAGNOSIS:

Melanotic neuroectodermal tumour of infancy.

DISCUSSION:

First described by Krompecher in 1918 (1). melanotic neuroectodermal tumour of infancy [MNETI] is rare and has variously been termed melanotic ameloblastoma, retina; anlage tumour, melanptic progonoma, emlanotic adamantinoma and pigmented epulis of infancy (2). To date there have been 200 cases of MNETI reported in the literature, with 33 located in the skull (3). The majority (70%) of these tumors occur in the maxilla and mandible (4). MNETI is a relatively benign tumour although local invasion and recurrences have been described as have occasional instances of frank malignancy (5). Wide surgical excision is the treatment of choice. Elevated serum catecholamines have been described in some patients with MNETI (6). Grossly, MNETI varies in color from gray to blue-black depending on the amount of melanin present. The MNETI is typically composed of irregular alveolar spaces lined by cuboidal cells containing melanin with other small, less well differentiated cells lying within the alveolar spaces or located in isolated nests within the fibrous stroma (7). Ganglionic differentiation may occasionally be seen (8). The presence of elongated cell processes emanating from the smaller, less well differentiated cells imply a neuroblast origin. Immunohistochemically the cuboidal cells express cytokeratin and melonoma-associated antigen (HMB-45) but are negative for S-100. Both cell types are typically positive for neuron demonstrates desmosomes with tonofilaments and neurosecretory granules present in the melanocyte-like cells (2). DNA analysis showing melanotransferrin expression in these tumors lends support for a neural crest origin for MNETI (9).